1. Field of the Invention
The invention relates to a mobile body discrimination apparatus in which an interrogator apparatus acquires data by non-contact communication from respective transponders, and in particular whereby such data are transmitted by modulated reflected radio waves
2. Description of Prior Art
Types of mobile body discrimination apparatus are known in the prior art, whereby continuous-wave (abbreviated in the following to CW) radio waves, at frequencies which are typically in the microwave or UHF (ultra-high frequency) range, are produced from an interrogator apparatus and are reflected by an antenna of a transponder back to the interrogator apparatus, with the reflection characteristics of the transponder antenna being modulated in accordance with information such as transponder identification information, so that the reflected radio waves convey that information to the interrogator apparatus. An example of such a system is described in Japanese patent HEI 1-182782. Other systems are known in the prior art whereby the DC supply power for operating the circuits of such a transponder is obtained by rectifying the radio waves received from the interrogator apparatus. Such an apparatus is for example described in Japanese patent SHO 63-5287.
Other types of systems are known whereby the interrogator apparatus is equipped with a directional antenna, which functions both to acquire data from transponders and to determine the size of a communication region (i.e., a region which transponders may enter and within which communication between a transponder and the interrogator apparatus is possible) in accordance with the level of transmission power of the interrogator apparatus. Such a system is described for example in Japanese patent HEI 6-71224. With another prior art system, spread-spectrum radio waves are transmitted by the interrogator apparatus to perform communication with transponders, as described in Japanese patent HEI 5-297131.
In the following, the prior art method described in Japanese patent HEI 1-182782 will be described, referring to the drawings. FIG. 70 shows the configuration of a transponder 80 of that patent, forming part of a non-contact type of discrimination apparatus utilizing radio waves. In FIG. 70, 81 is an antenna, 82 is an oscillator, 83 is an address counter, 84 is a PROM (programmable read-only memory), and 85 is a FET (field effect transistor). The operation of this prior art mobile body discrimination apparatus will be briefly described in the following. Unmodulated radio waves, generated from an interrogator apparatus which is not shown in the drawing, are radiated to reach the transponder 80. Electrical power is continuously supplied to the internal circuits of the transponder 80, by means such as a battery, etc. The oscillator 82 generates a clock signal which is counted by the address counter 83, to thereby generate successive addresses of the PROM 84. When a predetermined address is output from the address counter 83, the PROM 84 generates a code that has been predetermined as specific to the transponder 80. This can for example be an ID (identification) code, which is one of respective ID codes that have been predetermined for various transponders. The FET 85 performs ON/OFF switching in accordance with the ID code, to produce corresponding variations in the impedance of the antenna 81. In that way the transponder 80, by altering the impedance of the antenna 81 in accordance with the ON/OFF switching operations of the FET 85, produces corresponding alterations in the reflection characteristics of the antenna 81, whereby radio waves that are modulated in accordance with the information that is stored in the PROM 84 are reflected back to the interrogator apparatus. The interrogator apparatus can then demodulate the resultant received radio signal, to obtain the information from the transponder 80.
With such a type of transponder, since it is not necessary to provide any form of amplifier in the signal path within the transponder, the power consumption of the circuits of the transponder can be made small. Hence, by rectifying the radio waves which are emitted from the interrogator apparatus, it becomes possible to obtain power for operating the electronic circuits of the transponder, so that the transponder can be implemented such as not to require a battery or other power source. Various forms of such small-scale transponders have been proposed in the prior art, however the range within which communication between such a transponder and an interrogator apparatus can be performed depends upon the amount of power required to operate the circuits of the transponder. Specifically, the amount of power that is available for operating such a transponder is determined by the transmission power level of the interrogator apparatus, the directional characteristics of the antenna of the interrogator apparatus, and the rectification efficiency of the transponder, i.e., its efficiency in converting received radio waves into a DC power supply. In order to increase the size of the region within which communication can be executed between an interrogator apparatus and a transponder, the directional characteristics of the antenna of the interrogator apparatus can be set such as to illuminate a wide region with the radio waves which are transmitted by the interrogator apparatus. However such a widening of the antenna beam of the interrogator apparatus will result in a lowering of the antenna gain factor, so that the strength of the radio waves which are received by a transponder from that interrogator apparatus will be reduced, and the amount of electrical power which can be derived by a transponder will be lowered accordingly. If on the other hand the level of transmission power of the interrogator apparatus is increased, this may result in interference with other systems. Furthermore if the size of the communication region, within which communication can be executed between the interrogator apparatus and transponders, is made large, then the problem arises that a plurality of transponders may be concurrently within that communication region. Conflict will thereby arise between respective received signals that are obtained simultaneously from a plurality of transponders by the interrogator apparatus, so that reliable acquisition of information from the transponders becomes difficult.
Another example of a prior art type of mobile body discrimination apparatus is described in Japanese patent HEI 9-123919, which is a non-contact IC card system.
FIG. 71 shows the communication method of this prior art IC card system. With this system, if a plurality of IC cards 8601a, 8601b, 8601c are within the communication area of an IC card reader/writer apparatus 8602, the apparatus 8602 can access each of those IC cards. The reader/writer apparatus 8602 specifies an initial condition 8603, and timings at which each of the IC cards 8601a, 8601b, 8601c is to transmit a response data block 8604 containing the ID code of the card. The reader/writer apparatus 8602 receives each response data block 604 transmitted by the IC cards 8601a, 8601b, 8601c, and notifies these if data conflict occurs. If conflict occurs, the condition is changed by sending a retransmit request 8605 which specifies an altered condition.
For example the card 8601a transmits the response block 8606 after a time TO has elapsed following reception of the retransmit request, while the other cards 8601b, 8601c retransmit the response block 8606 after a time interval TO+T (ID) has elapsed following reception of the retransmit request. The reader/writer apparatus 8602 processes the response block that has been successfully acquired from the card 8601a without data conflict. The reader/writer apparatus 8602 then again sends the retransmit request 8607, and the card 8601b transmits the response block 8606 after a time TO has elapsed following reception of the retransmit request, while the other card 8601c retransmits the response block 8606 after the time interval TO+T (ID) has elapsed following reception of the retransmit request. By repetitions of such operations, response blocks are received from each of the cards 8601 without data conflict, and communication with a plurality of cards which are all currently within the communication region of the reader/writer apparatus 8602 is thereby achieved.
However with such a method of overcoming the problem of data conflict between transmissions that are received by an interrogator apparatus (i.e., the IC card reader/writer apparatus) from a plurality of transponders, when these transmissions overlap along the time axis, it is difficult to rapidly acquire data from the transponders that are currently within the communication region of the interrogator apparatus since it is not possible to acquire data concurrently from two or more transponders. That is to say, if data conflict occurs, then at least one transponder must then subsequently wait to receive one or more “retransmit” requests from the interrogator apparatus, and respond one or more times to these “retransmit” requests. Thus, such a prior art form of mobile body discrimination apparatus has the disadvantage that respective sets of data cannot be rapidly acquired by the interrogator apparatus (IC card reader/writer) from a plurality of transponders which are all currently within the communication region of the interrogator apparatus.
Another disadvantage of the prior art is as follows. If the internal circuits of a transponder are powered by AC line power, or by an internal battery, then it is possible to perform complex signal processing and to generate an adequate level of transmission power. However such methods are not appropriate with regard to achieving small size and light weight of a transponder, with low manufacturing cost and long operating life. For that reason, a type of transponder has been devised, for example as described in Japanese patent No. HEI 63-54023, whereby the power for operating the circuits of the transponder is obtained from radio waves that are directed to the transponder from an interrogator apparatus.
FIG. 72 shows the general features of the transponder which is disclosed in that patent. Here, microstrip lines 902 each having a length that is one half of the wavelength of the response signal, and a flat patch type of microwave antenna 8903 are formed by metallizing on a substrate 8901. Microwave radio waves which are received by the antenna are rectified by the diode 8904a, while a response signal is applied to diodes 8904b to be transmitted.
However with such a prior art arrangement for obtaining DC supply power to operate the circuits of a transponder, in order to maximize the amount of energy that is converted to DC supply power by the rectifier element, it is necessary to provide some form of impedance matching circuit for matching the impedance of the antenna to that of the rectifier element. In the prior art, such a matching circuit has been implemented (e.g., as a fixed length of microstrip) on the assumption of using a rectifier element (such as the diode 904a in FIG. 71) which has predetermined standard characteristics. As a result, due to the manufacturing variations which actually occur in the characteristics of such diodes, it has not been possible to ensure that the energy of the received microwaves is efficiently converted to DC power.
Another disadvantage of the prior art technology is as follows. A prior art type of transponder which functions as a non-contact IC card, i.e., which can transmit and receive data to/from an interrogator apparatus (referred to as an IC card reader/writer apparatus) is described in Japanese patent No. HEI 8-252995. FIG. 73 shows the configuration of this prior art non-contact IC card. This has a substrate 7901 having a connecting lead pattern 7902 and an antenna 7903, for performing transmitting and receiving, formed as a patterned portion of a conductive layer on an upper face of the substrate, an insulating spacer 7904 having an aperture 7912 and a through-hole connector 7906 formed therein, and having a ground pattern layer 7905 (i.e., an electrically conductive layer which is connected to the ground potential of the circuits of the IC chip 7907) formed on an upper face 7904a of the spacer, an adhesive film 7911 formed with apertures corresponding to the aperture 7912 and through-hole connector 7906, for attaching the upper face 7901a of the substrate 7901 to the lower face 7904b of the spacer 7904, bumps 7908 (i.e., protrusions formed of a material such as solder, formed on a flip-chip IC to serve as connector elements to the internal circuits of the IC and for attaching the IC to a connecting lead pattern which is formed on a substrate) disposed in the aperture 7912 of the spacer 7904, an anisotropic electrically conducting adhesive material 7909 for attaching and electrically connecting the circuit pattern 7902 to the bumps 7908 of the IC chip 7907, and an epoxy type of molding material 7910 which fills the spaces between the aperture 7912 of the spacer 7904 and the IC chip 7907.
Such a non-contact IC card can be used as a transponder of a mobile body discrimination system, in which case the IC card will be attached by its front or rear face to some article, which might for example be formed of metal. In such a case the problem arises that while the reader/writer unit should be able to receive data from a card irrespective of the direction of orientation of the faces of the card, if the IC card has some object located close to the rear face of the card (i.e., the outer face of the substrate 7901), then the antenna 7903 may become substantially or completely shielded from incident radio waves. Thus, deterioration of the performance of the antenna 7903, and hence a deterioration or complete interruption of communication operation, can occur. Hence, such an IC card is not suitable for use as a transponder which may be attached to a surface of an article with the outer face of the substrate 7901 in proximity to that article.
In the following description and in the appended claims, the term “mobile body discrimination apparatus” will be used to signify a combination of an interrogator apparatus with a plurality of transponders which are designed to operate in conjunction with that interrogator apparatus, while the term “mobile body discrimination system” will be used to signify an overall system which includes such a mobile body discrimination apparatus in conjunction with means for effecting relative movement between a plurality of objects and an antenna (or plural antennas) of the interrogator apparatus, with each of the transponders being configured for transmitting data relating to the corresponding object to which it is attached. Also, in the following description and in the appended claims, the term “scanning” of a plurality of transponders by an interrogator apparatus is to be understood as having a significance which broadly covers the concept of effecting relative motion between the interrogator apparatus and the transponders such that a successive transponders are brought within the communication region of an antenna of the interrogator apparatus. This motion may be continuous or it may be intermittent, for example the relative motion between the interrogator apparatus and respective groups of one or more transponder might in some cases be temporarily halted. In addition, the relative motion may be effected by moving the transponders with the interrogator apparatus held fixed in position, or by moving the interrogator apparatus with the transponders left in a stationary condition.
Furthermore in the following description and in the appended claims, unless otherwise indicated, the term “spread-spectrum radio waves” is to be understood as signifying spread-spectrum radio waves which are not modulated to convey information.
In addition, the term “directivity” is used herein to signify the direction of an axis of maximum antenna gain, of a directional antenna.